package jdbc;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

/**
 * 别名
 */
public class JDBCDemo6 {
    public static void main(String[] args) {
        /*
            查询1年级1班一共多少人
            SELECT COUNT(*)
            FROM class c JOIN student s ON c.id = s.class_id
            WHERE c.name = '1年级1班';
         */
        try (
                Connection connection = DBUtil.getConnection()
                ){
            Statement statement = connection.createStatement();
            String sql = "SELECT COUNT(*)" +
                         " FROM class c " +
                         "JOIN student s ON c.id = s.class_id " +
                         "WHERE c.name = '1年级1班'";
            ResultSet rs = statement.executeQuery(sql);
            while (rs.next()) {
                int count = rs.getInt("count");
                System.out.println("人数:"+count);
            }
        }catch (SQLException e){
            throw new RuntimeException(e);
        }
    }
}
